Therapy-related myelodysplastic syndrome (t-MDS) or acute myeloid leukemia (t-AML) is a late complication of cytotoxic therapy of both malignant and non-malignant diseases. Characteristic recurring abnormalities of chromosomes 5 and/or 7 are frequently noted in t-MDS/t-AML. In our updated series, we observed loss of 5q or 7q in 214 of 306 (70%) patients examined. In previous studies, we delineated a 1.5 Mb segment of chromosome 5 within band 5q31, between markers D4S479 and D5S500, that was deleted in all patients examined, and prepared a partial genomic contig of the commonly deleted segment. In the current granting period, we generated a complete genomic contig, and a partial transcript map of the commonly deleted segment. We hypothesize that a tumor suppressor gene located within this segment may play a role in the pathogenesis of this disease. We now propose to use a positional and candidate gene approach to identify a myeloid-leukemia gene in 5q31. In Aim 1, we will use several experimental approaches to generate a complete transcript map of the commonly deleted segment. In Aim 2, leukemia cells characterized by abnormalities of chromosome 5 will be examined for mutations of these candidate genes. If mutations of a gene on 5q are identified, we will determine the spectrum of mutations in myeloid leukemia cells, determine whether mutations of the gene are somatic or germline, and identify the consequence(s) of the mutations on the function of the gene/protein (Aim 3). In Aim 4, we will evaluate alternative mechanisms in the pathogenesis of t-MDS/t-AML with abnormalities of chromosome 5, including the evaluation of epigenetic mechanisms for gene silencing (DNA methylation); we will also use in vitro models to evaluate the role of haploinsufficiency. To facilitate Dr. Shannon's efforts to identify a myeloid leukemia gene on chromosome 7, we will seek to refine the commonly deleted segment of 7q22 by using molecular cytogenetic mapping techniques to map the deleted segments in patients with loss of 7q (Aim 5). Tumor suppressor genes have not been well-characterized in the hematologic malignant diseases. We hope that by analyzing recurring deletions, we can begin to evaluate the role of recessive mutations in the pathogenesis of MDS and AML, and to elucidate the relationship of previous cytotoxie therapy with mutations of genes on chromosomes 5 and 7.